The present invention relates to rotary fluid pressure devices, and more particularly, to such devices that are provided with a single-speed option and a multi-speed option.
Although the present invention can be used in connection with various pump and motor configurations that include various types of fluid displacement mechanism, such as a cam lobe type, it is especially advantageous when used with fluid motors having fluid displacement mechanisms of the gerotor type and will be discussed in connection therewith. While the present invention may also be used in connection with fluid motors having various types of valve arrangements, it is especially advantageous when used in connection with fluid motors of the disc valve type. Therefore, the present invention will be discussed in connection with disc valve gerotor motors without intending to limit the scope of the invention.
Fluid motors of the type utilizing a gerotor displacement mechanism to convert fluid pressure into a rotary output are widely used in a variety of low-speed, high-torque commercial applications, such as skid-steer loaders. One common use for fluid motors in low-speed, high torque commercial applications is vehicle propulsion, wherein the vehicle includes an engine driven pump which provides pressurized fluid to a pair of fluid motors, with each motor being associated with one of the drive wheels.
For many years, vehicle manufacturers have provided vehicles with the option of fluid motors capable of operation in a low-speed, high-torque mode only (single-speed motors) or with fluid motors capable of operation in both low-speed, high-torque mode and high-speed, low-torque mode (two-speed motors). While choosing between a vehicle with either single-speed propulsion motors or two-speed propulsion motors for vehicle applications enables the vehicle manufacturer's customers to choose the best vehicle for their particular needs, this propulsion motor option creates some difficulties for the vehicle manufacturers. One such difficulty is that the manufacturer is required to maintain two part numbers for motors used on the same vehicle model. In other words, the manufacturer must maintain part numbers for a single-speed version of a propulsion motor, as well as a two-speed version of the propulsion motor in order to accommodate the option choice of the customer. While the single-speed motor and the two-speed motor are not identical given that one is capable of only single-speed functionality and the other is capable of two-speed functionality, the motor mounting, displacement, valve type, output shaft, and porting type are typically the same.
Another difficulty that vehicle manufacturers have in providing this option to customers is that this option requires manufacturers to have accurate build orders early in the assembly process. Typically, fluid motors are assembled onto the vehicle frame very early in the assembly process. Many times, the fluid motors are installed on the vehicle frame before the build orders have been placed. Therefore, if the assemblers are building single-speed versions of a vehicle and incoming build orders, which were submitted after assembly had started, require two-speed versions of the vehicle, the single-speed fluid motors must be removed from the partially assembled vehicle and replaced with two-speed fluid motors. This becomes difficult because after the fluid motors and other vehicle components have been assembled to the frame, access to the mounting surfaces of the fluid motors is limited.
In addition to these difficulties, some vehicle manufacturers receive requests from customers to “upgrade” their current vehicle, which is configured for single-speed functionality, to a vehicle with two-speed functionality. While vehicle manufacturers have done this successfully in the past, the removal and replacement of the single-speed fluid motors with two-speed fluid motors is a labor intensive task.